campbell



A ril 27,1926. 1,582,334

W. L. CAMPBELL AUTOMATIC SWITCHING A ND TELEPHONE SYSTEM Filed June 19, 1905 5 sheets sheet 1 April 27 1926. W. L. CAMPBELL AUTOMATIC SWITCHING AND TELEPHONE SYSTEM 5 sheets-sheet 2 Filed June 19, 1905 al l l t l l l bw Q:

www www wvw 5 Sheets Sheet 5 H m r% W. L. CAMPBELL AUTOMATIC SWITCHING AND TELEPHONE SYSTEM Filed June 19, 1905 April 27 1926.

w a w 6 M a M M owwwmwmwwfi 9 o\ O "a 0212i) W 7.... m d QFDU/ a :u 0 m L 6 W 7 J 4 w Z 4 m H L I] 4 6 a 3 0 0 W W 5 A ril 27,1926 1,582,334 W. L. CAMPBELL AUTOMATIC SWITCHING AND TELEPHONE SYSTEM Filed June laggyy l 5 sheet s sheet 4.

We 7 %%%W April 27,1926. 1,582,334

W. L. CAMPBELL AUTOMATIC SWITCHING AND TELEPHONE SYSTEM Filed June 19, 1905 1 5 sheets sheet 5 fkwwzCiw m Patented Apr 2?, liiiib.

insane l/VILSQN L. CAM?BELL,- 01* CHICAGO, ILLINOIS, ASSEGNGB, BY MESNE ASSIGNMENTS,

'lO AUTUMATIC ELECTRIC INC OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- "WARE.

AUTOMATIC SWITCHING AND TELEPHONE SYSTEM.

application filed June 19, 1905. Serial No. 65,955.

'1 0 all ctr/tom 2'5 may concern:

Be it known that I, VVttLsoN L. a citizen of the United States of America, and resident of Chicago, Cool; County, Illinois, have invented a certain new and useful Improvement in Automatic Switching and Telephone Systems, of which the "following is a specification.

My invention relates to automatic tele phone systems of that particular type in which any calling subscriber may connect his line with that of any other subscriber by momentarily and successively establishing a number of ground-circuits, so as to transmit to the exchange or central station a number oi electrical impulses corresponding to the digits of the number of the called subscriber, these electrical impulses being employed for producing a stcp-by-stcp operation on the 'part of one or more switching machines at the said exchange or central station, whereby the apparatus as a whole is under the control of any calling subscriber for thepurpos of picking out and, connecting some other subscribers line with his line, provi" ing, out course, that the called subscribers line is not busy. More specifically con sidered, my invention relates to automatic telephone systems 01" the foregoing general character in which the switching machines are of two kinds-that is, divided into two general classes, one general class being known as selectors, the other general class being known as connectors, and the class of selectors then being divided into subclasses, so to speak, according to the size of the exchange, one sub-class being known as first-selectors, and the other sub-class being known as "second-selectors. As is well liIlO'Y-Jll, a selector consists of an electrically-propelled and step-by-stepsactuated switching machine which may be employed by a calling subscriber for picking out a certain group oi? trunk-lines, but which ceases in a measure to be under the control of the calling subscriber as soon as the desired group of trunk-lines has been located, and which then proceeds to pick out an idle or non-busy trunk-line, it being understood that, as tar as the calling subscriber is concerned, any one of the trunk-lines in such group will serve his purpose Ontheother hand, a.connector is also an electricallypropelled and step-bystep-actuated switch CAMPBELL,

ing machine adapted to be employed for picking out a certain group of lines; but in this case, it is a group of subscribers lines which is picked out, rather than a group of trunk-lines; and, furthermore, a connector is also distinguished from a selector in this respect,to-wit, that it is under the control of the calling subscriber throughout its entire operation-that is, it is not only controlled directly by the calling subscriber for that part or its operation during which it picks out the particular group of subscribers lines, but it then continues under the direct control of the calling subscriber while it is pickin out or locating the particular subscribers line with which the-calling subscriber desires to connect his line. There are, of course, and as will hereinafter more fully appear, certain operations which are characteristic of both of these kinds of switches, and which are strictly automatic and not under the control or management, so to speak, of the subscribers. For example, in an automatic telephone system of this character it is essential that the selectors be equipped with automatic means for preventing their wipers or switching-arms from stopping on the contacts or terminals which are connected with trunk-lines already in use, and in a connector it is essential that automatic means be provided for precluding the possibility of making connecti-on with a subscribers line which is already in use, or which is in electrical connection with some other line. Again, the releasing ot the different switches, while brought about by some act on the part ot the :alling or the called subscriber, is throughout oi a more or less automatic nature, it being common to employ devices and circuits oi such character that the mere act on the part ot' either subscriber, in hanging up his receiver, serves to automatically disconnect the two lines, and to restore all 0-: the switches or switching machines which have been retained in operation between the two subscribers.

(Zirenerally stated, the object oi my invention is the provision or an improved, simplifiedand highly efficient automatic telephone systcm of the foregoing general character.

Special objects of my invention are the provision of an improved construction and.

arrangement whereby it will not be neces methods of operation which characterize the" old systems, wherein each selector-was provided with a side-switch, to provide an improved construction and arrangement whereby certain other more or less objectionable features may be dispensed with, as, for example, the so-called dead resistance which has always been included in series withthe release relays of the selectors, it having been the practice prior to my in vention to connect the release-relay of the firstselectoi in series with the dead-resistance-coil of the second-selector, whereby the two coils are employed in series in the relerise-circuit extending between switches to provide an improved construction and arrangement whereby an eff cient construction and mode of operation, and the desiredresults may be obtained by simply connecting the release-magnet of one selector in series with the release-relay of another selector, and whereby each release-magnet of the second-selectors, or of the connectors, forxexampl-e, constitutes the required resistance between one terminal of the battery and one terminal of the release relay of another switch, thus giving each release-magnet a double function, so to speak, and thereby insuring more econom cal results than would be obtained by using separate additional resistance-coils; to provide an improved construction and arrangement whereby the shaft-cam ordinarily V employed merely as a stop for limiting the motion of the side-switch can be retained in the structure as a whole, notwithstanding the elii'nination of the side-switch from the machine, andemployed as a means for open ing, and closing some switch s ti jngs which constitute a new feature in a switching machine of this general character; to provide certain improved circuits and circuit arrangements, together with certainnovel and advantageous combinations, as hereinafter described and claimed; and to provide ce.r-

tain details and features of improvement tending to increase the. general efficiency and serviceability of auton'iatic telephone switchi-ng apparatus of this particular character.

To the foregoing and other useful ends, my invention consists in matters hereinafter more fully set forth and claimed.

In the accompanying drawings, Fig. l, in connection with Fig. 2, is a diagramn'iatic representat-ion of the switching apparatus and circuits involved'when a siibscriber at a sub-.

station A (Fig. i) has established connection with subscriber at a'sub-station S, desig- E, together with their respective bank terminals As indicated at'sub station A, each subscriber is provided with a telephone having a ringer 1, a receiver 2, and a switch-hook 3 which controls the positions of a number of springs e, 5 and 6; 7 and 8; 9 and 10; and ll, 12 and- 18. There is also a transmitter 145, a local battery l5, and an induction-coil 16 with primary and secondary windings 17 and 18, respectively. of any approved or suitable design, and 1s Fhe calling device is represented by two p'uslrbuttons 1S) and 20, 7

together with two springs 21 and 22, and three contact-points 23, 2e and A sigi'ialing-button Q6 closes a circuit through either of two contactpoints 27 or 28iby way of an interposed spring 29.-

The sub-station is connected with its first-selector C by thetwo lii econductors 30 and 31'. Referring to the firstselector, represented in Fig. 3, a so-called vertical line relay" is normally connected to the vertical-lineconductor 2300f substation A. When this relay isenergized, it actuates its armature 36, and in this way the position of the springs 37 and 38, relative to two other springs 39 andv 40, is controlled or determined. with. the rotary-line-conductor'31 of sub station A is a so-called "rotarydine-relay" 41, which is also provided with an armature.

42. This armature is also designed to operate two springs 43 and 3Q=with respect to two other sprin' s l0 and 37. A so-called vertical-magnet a5 is coii'iposed of two coils 46 and 4-7. These coils, when energized, attracttheir armature L8, which lat ter is providedwith pivots 4:9 and 50 that supportit' on the switch-frame. From this armature there projects an arm 51 retained in normal position by a retracting-spring 52. An L-shaped piece Y53, and a soscalled vertical-pawl 541., which is also controlled by a retracting-spring 55, are foundon this arm. Another operating electro-inagnet is the so-called rotary-inagnet 58 with its two coils 59 and 60, which control the rowry-armature! 61. This latter armature vibrates about its supporting-pivots 62 i and Gdand is normally controlledibyn.retracting-spring 64-. Said armature has attached 'lated from shaft, but within reach t number of arms, whereof the arm lii'lOTv'l'l as the interrupter-arm and eno' ges, at proper times, the so-called intermuster-springs 66 and 6?; another is the socalled retary-armature-finger" 68 that works Said armature, ooorted from the sua 's l and T8, and is held normally lv a retracting-sprin 79. This spring is hell in place by a lug 80, and is ordinarily in electric contact with spring 81, from which latter it when the release- In addition, there armature is attracted. is attached to this armatu e a so-calied release-link 82, the forward end of which latter is provided with an opening that engages with so-called double-dog 81,

through a pin 85, when the switch is red. This double-dog is equipped Vltll the following details: Two pivots 86 and 8?; tr: %,11118 88 and 89; and a relracti g-spring 90, which latter controls the posit-ion of said double-dog while the switch is in use. i-inother magnet 91, known as the private-1nagnet, also has an Lillllture 92 which it operates. The usual pivots 933 and support this armature, and it has an arm 95 that operates a number 01 sorings 98, 97, 98 and 99. ()no of the distinguishing features of a switch of this kind is the shaft 100. lhis shaft is provided with set of circular teeth 101 which are traversed by a channel 102 into which normally projects the end of a shaft-rest-arrn US; and with a set of longitudinal teeth The te th 101 are called the vertical-- teeth, as they are used for giving the shaft a vertical movement, while the teeth 10 1 are called the rotary-teeth, as they are used. tor giving the shaft arotary more meat. On the upp r end of said shaft there is a coil-spring 105, one end of which, is attacl'ied to t1,11-U111lll-}')0$i3 166. Just below this there is a norn il arin 107 which has supervision over a spring 108, the latter usually being in contact with contacepoint 109. Near the lower end of the shaft, the private-wiper 110 is supported and insu of which wiper is the private-bank 111. tritill lower are the line-wipers 112 and .1153, which are separated from each other, ane from the shaft, by a suitable insulation 11 1, and opposite whi is situated the line-lrank 115. A earn attachment 11-8, justbelow the longitudinal teeth, through the means of an insulating;- piece, controls the connection between the so-calicd cainsirinu's i111 elect 11'! and 118. roanagnet 120, known as the ouch-role*se--elay has an armature 121 that operates a spring 122 with respect to a second spring 1213. it relav 125, known as the lineswitchia relay is shown, the a mature of which controls certan circuits throu h the inejean duun ot a number 01 springs 1%, 1:28, 13-"), 181 and 132.

The second-selector is almost the same as the first-selector, and is represented in Fig.

The Yerticalhne-rciay 185, with its arice,

1! 189, 1310 and 14-3, and the rotary-linerelay 1 1-1 with its armature 1 12, are identical. The verticalanagnet 1&5, the coils 146 and 1 17 oi? which control the vertical-arniature 1&8, is also the same. In connection with such an armature, the pivots 1 1% and 150, and the vertical-arm. 151., have been referred to; and in connect on with the vertical-arm, such part as the retracting-spin11g 152, the l.-shaped piece 153, the vturticulpawl" 151- with its retracting-spun 105,

have been explains l. The rotary-in 158, and rotaryunagnct-coils and 181) with their armature 161, are similar to those shown in Fig. 3. This armature also 'ibrates about its pivot, 162 and 163, and is subject to the tension of a retracting-spring 161. lit has the familiar arin known as the interruptenarin 165 which operates the interruptor-springs 166 and 167; the 1'OtJ.1:y'l11111 tine-finger 168; and the rotaryr111 18.), which latter carries the rota ry-pawl 170 normally inder the tension of the pawlretracting-spring 171. The release-magnet 175, the armature 176 of which is supported from the switch-frame by the pivots 177 and 178, restores the second-selectorswitchY A retracting-spring 179, normally engaged with a lug 180, is ordinarily in electric contact with a contact-spring 181, and holds the rrnature in a position of rest. T he relcas link 182 is also provided with an opening 183 adapted to engage the lug 185 on the double-dog 181. The douhledog is provided with the usual pivots 186 and 18? about which it vibrates; two locking-arms 188 and 189; and a rctractin r-spring 190.

not"

The private-magnet is shown at 191. Its

armature 192 is usually supported from the private-111agust-frame by pivots 198 ai d 19%, and is provided with an arm 1953 which controls the so--called private-sprinas 196,

V and the cam 21 i which, in this case, operates three springs 215, 21.6 and 217 through the medium of an insulating piece. The electromagnet- 220, which is known as the baclb release-2nagnet, and its armature 221 that controls two springs 222 and 223, are tally shown. The 'line-switching-relay 225, through its armature 228, controls a nunibcr of springs 227, 228, 229, 230, 231 and 282.

The connector E has a number of parts similar to those of the first and second seleo tors such, for instance, as the vertical-line relay 235 and the rertical-line-relay-armature 236; the lined'elay-springs 28? and 238, 239, 2-ft0 and 2453; and the rotary-linerelay 24:1 with its armature 2&2. The vertical-magnet 245, with its coils 246 and 247, controls the vertical-armature 24:8,v

which latter is, as usual, it: stened to the switch-frame by the pivots 24.9 and 250. in an armature or this type, the vertical-arm" 251, the retracting-spring 252, the L-shaped piece 253, the

vertical pawl 25 5;, and the pawl-retracting-spring 255 have already been pointed out. The rotary-magnet 258 also has two coils 259'and 280 which, when energized, operate their armature 201 in an oscillatory manner about its pivots. 262 and 263, against the tension of a retracting spring 26%. Said armature is, however, only provided with one arm, to-wit, the rotary arm 265. On the forward end of said arm there is attached the usual rotary-pawl 268, which is subject to the tension of a retracting-spring 267. The release-magnet 268, the armature 209 of which moves about the pivots 270 and 271, attracts said armature against the tension ot the retractingspring 21 2. The release-link 278, which is rigidly tastcnedjto pin 27% is provided at its forward end with an aperture 275 designed to engage normally with the locking; double-dog" 270 by means of the his; 277;

This double-dog is the same as that of the first and secondelectors. It is provided,

as usual, with pivots 278 and 279 about which it oscillates, with the two lockingarms 280 and 281, and with the retractingspring 282. The privatednagnet 288 has an armature 284: which also oscillates about two pivots 285 and 286. Said armature is provided with an arm 287 whicli is subject to the tension of a retracting-spring 288. This arm is provided with two flexible springs 289 and 290, on the forward ends of which there is an eseapement termed by'a number of teeth 201, 292, 293 and 29 i; and a lateral arm 295 which controls four springs 29.0, 297, 298 and 299. The usual switchshaft 300 has its circular teeth 301 slotted at 302; has a shaft-rest 303; has the longitudinal teeth 304; has a. coil-spring 3.05 at taclicd to a normal post 306; and has a 1101'- nial arm 30? con'l'rollingthe springs 308 and 309, The privatewwiper 310 associated with the "prirate-bank 311, the linewipers 312- and 31.3 associated with the linc-banleterminals 315, and the cam 816 near the center of the shaft, are all well known. In addition, there is associated with the connector an arm 820 known as the side-switcharm, the latter being subject to a retracthag-spring 821; On this arm there is a lug 322 near one end, and near the other a sh'aitt 323 on which are mounted a number of wipers 324:, 325, '326'and 32. which are adapted to engage a number of conta *t-points 328, 332 and 336; 329, and

33?; 3210, and and 331, and 389, respectively. Between the shaft supporting these wipers and the lug 822 are the; sideswitch-arm-pivots 340 and 341 and a lateral arm 842. To this latter ,211'111 342 there is pinned another arm which engages the doulile-dog 2% through the medium ot another arm 7 with all its parts,

is known 'as the hideswitch. lh'is side-switch may be made to I assume either oi three positions.

In the third position, the right-hand end or" the "side swltcn-arni 820'rests against a lug The side-switch-arm,

345. The connector has, in addition, two

coils mo and that constitute a bacle release-relay and the armatures 349 and 353 of which, when depressed, close together the connectorback-release-springs 350, 851 and 35%. A ringer-relay 358 is'provided with an armature 359thr0ugh which it operates a number of springs 360, 381, 3 62,

863, 304: and and there are two condensers 306 and 367 wnich appear in the talkingmiifcuit. In Fig. 2, the firstselector F of the called subscriber is identical in make-up with the filSbSBlOOtOl C of the calling subscriber. It has the switchshai t 370, the circularand the longitudinal teeth 3'71 and 372, respectively; the private wiper and the linewipers 374i and 375; the cam 8Y0 and the canrsprings 377' and 378; and the normal arm 379 which c0111 trols the two springslSSO and 381. jlhe vertical and the rotary line-relays385 and 386 are shown, with the springs they control-'387, 388, 889, 390 and 391 as well as the line-switching-relay-springs 392,

"893, 894-, 395, 390 and 39? that are under the control of the line switching-relay 398.

rotaryare two circuit-interrupters 406 and a 407;

and an induction-coil 408 with primary and secondary windings 409 and 410, Having thus do cribed the mechanical details, it remains to describe their functions in connection with the circuits of the system.

In the 'draai'ings, battery is represented in a number of places; but it will be understood that this is oiiily for convenience of illustration, there beii in reality only one battery with its positive terminal preferably grounded. it may assumedthat the switching apparatus is in its normal condition, i lustrated in Figs, 3, 4 and 5. Now, if a subscriber at sub-station A (Figs. 1 and 2) wishes to establish connection with subscriber at sub-station S, designated as 2241, he will first remove his receiver from its hook and operate his calling device four times, corresponding with the digits 2, 2, 41 and 1. hen the receiver 2 is removed from its hook 3, the latter rises under the tension of a spring (not shown), breaking contact with spring -1 and closing contact between the springs :3 and 6,7 and 8, and 9 and 10. 'lhe closing of the last two places contact-point in direct connection with the ground (1 through the following circuit: from contact-point 25 to conductors 120 and -21, to springs 9 and 10, and to ground G The subscriber will then proceed to press push-button 19 twice, with the result that spring 21 breaks contact with point 23 each time, and grounds the vertical-lineronductor 8O twice by putting it in connection with contact-point 25. The result of grounding this conductor twice, momenta rily, is that vertical-line-relay of the first-selector C is energized twice through the following circuit: from ground G at sub-station A to contact-point 25, to vertical-line-conductor" 30, to springs-128 and 127, conductor vertical-line-relay 35 to conductors l23 and 42 1- to the non-grounded terminal of battery B, to ground G. 'ihus energized, said vertical-line-relay actuates its arn'iature 36,thereby causing springs 38 and lO to come into contact twice, causing the vertical-inagnet-coils 416 and 4:7 to be energize-d twice in turn through the following circuit: from ground G through springs 4.0 and 38, conductor 125, verticalmagnet-coils db and 17, conductor 426, springs 81 and i9, conductors 127, 428 and 42% to the non-grounded terminal of battery 13, to ground G. Thus energized, the vertical-niagnet 15 attracts its armature 48 which, by means of the arm 51, causes the "vertical-dog" 51 to engage with the circu- ,1 10.1, raising the shaft two steps. the first impulse of the armature 18, the

t L-shaped piece 53 on the arm 51 disengages the release-link 82 from the double-dog device 81, allowing the arm SS under the tension of the retrochug-spring 90 to engage with the circular teetln loclting the shaft in raised position. At the second impulse, when the shaft is raised the second step, the same arm 88 holds the shaft in its second position. After the shaft has been raised two steps, the private-wiper 110 and the line-wipers 112 and 113 will be found on a level with the first contact of the second row of their respective banks 111 and 115. After this has been accomplished, the subscriber at sub-station A presses the button 20 once, thereby grounding the rotary-line-conductor 31 once by bringing spring 22 against grounded contact 25 after the former has broken from contact-point 2-61. The result is that the rotary-line-relay 11 of the first-selector" C is energized once through the following circuit: from ground G as before, through contact-point 25, spring 22, rotary-line-conductor 31, spr' igs 131 and 130, conductor 129, rotaryline-relay. 411, conductors 4123 and 1-24 to the non-grounded terminal of battery 13 and to ground G. Thus energized but once, the rotary-1ilieu-clay 11 actuates its armature 412, bringing springs 43 and 410 together, thereby energizing the privateunagnetf.,91

once through the following circuit: front ground G through springs 10 and 13, conductor 130, private-magnet 91,conductors 4:3 1 and 4-26, springs 81 and 79, conductors 1,27, and 124 to the non-grounded terminal of battery B and to ground G.

Thus energized, the private-machet attracts its armature 92 which, by means of its arm 95, causes springs 97 and 98 to disengage and to momentarily come into contact, respectively, wit-h springs 96 and 99. soon as springs 96 and 97 come into contact, a circuit is closed through the rotary magnet-coils 59 and 60, as follows: from ground G through contact-point 109,

spring 108, conductor 4132, springs 9'? and 96, springs 67 and 66, through rotary-ma net-coils and 59, conductors and to the non-grounded terminal of battery 13, to ground i i hen the rotary-nuignet is energized, it attracts its armature 61 which, tl'irough the inediun'i of the r titre-finger {$8, prevents the prlv .--arm at-ure 92 from at once regaining its normal position, thereby preventing springs and 97 from breaking contact oefore the desired time. The said armature 61, on being attractec, also causes interrupter-arm G5 to separate the springs (56 and 6?, thereby breaking the energizing circuit of the rotary-magnet 58. As soon this occurs, the rotaryarmature returns to its normal position due to the strength of the retract ing-spring tll-allowing the sprii it} and 67 to re-engage, but not until ter the rm tary -armattire-linger (59 has yrinitted the private-magnetarinature 923 to fall back suiiiciently. under the tension of the spring 9", to allow springs 97 a11d96 to Septiiliile the intcrrupternrn and the re tary-arniatare-finger perform their wor' guard over said ennui;

ing circuit: from grounded terminal of battery B to occupying-switch and circuit (not shown) to the first cont-set otthe second roe ofprivste-banlz 111 to private- Wipei. 110, conductor melt-relense re- A 1h I: lay 120, conductor +131, sp i m to pri gnet? 91 486 springs 81 1nd "3"?) l nul of bat ery 1). i.

. and 1-2 it 21) n1- and 1:4;

' "I energizuh the ori vote-magnet 91 at its mnature 92,

l tr f 2* r of its relievingl? d at even otter =tureme 1 the inter-rep 1 bn'ilren the energizing circuit throng" rotary inagno 58, by separating;- sprin 6S and GT, and oh loving the rotary--urinetin-e 61 to regain its normal position, the n'ivnte-srinature 92 is still held down. l n tli 9s 96 and 94 are rots ned 1 2") tthrough more, rotating the short end the priru ewiper 110 to the tenh eon not. As soon u es with the 1 us the private-Wip r thong;

v 1 w ninth contact, the circuit through the privute-inegnet 91 is broken 2111 the mi 1 "vote-armature 9:1 is restored to the (are of the rotarv-nrn,etin'e-lin ei 68. its soon as hie in. r u, A. were 30 )lel 7 "5 ti te r )ter l e he oontie of spmne's and GT the a "store to [,r the hast tune,

turns to its normal esition T 1e 92 to reperinitting the privnJe-m'innti turn with it. The rupt r-springs (i6 and 67 again one -ut not until utter privntesprings d 2 have disengaged. The last 9? then comes in contact with the 98 which in turn has also disengaged 11' another spring 99.

At the end of this operation, the can]- springs 11'? and 118, having engaged in eontuet after the shaft has been roti ed one. as soon as the private-armature allows springs 96 and 9'? to separate, the line switchingeehiy 125 is then energizech in the manner elrenty des ribed, thus ope'ating the springs which are controlled through armature 1126, es before. Thus it will be seen that the first-selectofi, R13 the end of its operation, has anton'nitieslly selected an the oonduetors of 111611-- idle trunk-line 4: 8 and i-39lesr to a seeonoeeieetor I 3 1 has extended the to me some in n manner previously described; has estuhhshec guarding POtGlltlRl at the tenth in the second row oi? privatebank contact ythe closing; of springs 97 and 98 as 111, b ahead operating coils that ordinarily rested across the suhse "ibers line by separating the springs 1:1 and 128 from springs 1530 and 12? at t] e moment that the "dine-switchingi'elny 12 is were zed. It will be remembered that While ie "private--Wiper 110 was passing over contact-points supplied Win11 guarding potential, the priveteenngnet 91 was energized through a circuit that included the relay is so designed that under these eonditions its niag netie e1" r izotion not sutioient to attract the armature 121 against he tension of the spring As soon as he first-selector O has emended its lin to the second-sol wtor D, and o guarding V is established at the private- Wiper 110, a circuit established over the p ivatetrunl e ll-2 that energizes the iine-switehing-rel2W7 two at the second- SGlBCtOl throi 31 thei' ollowing circuit: from gonmhterininzil it of battery B to ground at tint-selector C to contact-- point 109 spring; 108, conductor 132, springs 97 and 98, conductor .3 1, b:ioh-Yeleaseu'elay 120, conductor 4:411, private-Wiper"? 110, private-trunl-;-eonduotor 1 12, conductor 155 of second-solester D, coin-springs 21? and conductor 150 iins-switching-re lay 225, conductors 7, 1 15 and 4 18 to the non-grounded tel Qnal o-t battery 13. As soon as the iirsoseleetor C outs in on the trunk leading to the second-selection l) the lineswitehingrelny 225, being thus energized, attracts its armature causing;

springs 228 and 231 to disengage from springs 289 and 232 and to engage with springs 22? and 280, respectively. in this Way the vertical and rotei line-relaws 0;? said seeond-seleetor he re bridged urross the main line onduetors and 4-38 leading "to sub-station A. The subseri e sub-station A lun'ing; thus, by the 1 l lHS :z1ll1n o; ;lev1ce in a manlnlllalplllt iiflh o 1 onding to the first digit of the n 11.11111 er 7352 i t 1 t1, whiel he is ceiling, connected on ido seeondselectorl he by on L 19 twice. 1 iis dnetor oiiee 1112' the ver eehli oihihseieetor" D ing eil'enit: 1 A to oron vice tin-on.

128111161 I I enldinem'iper if. I i

i 228 and 522?. eondifi y described; and has disconnected the i,iiolerelease-relay; but this tery B, and to ground Gr. Thus energized, the rertical-line-relay of the secondselector D actuates its armature 136, thereby grounding the spring 138 with groundspring 140, and in turn energizing the vertical-magnet twice through the follow ing circuit: from groundG to springs 140' and 138, conductor 447, vertical-magnetcoils 146 and 147, conductor 448, springs 181 and 179, conductor 449, to the nongrounded terminal of battery B, and to ground G. This vertical-magnet operates its armature 148 for-the purpose of raising the shaft 200, as in the case of the firstselector C. On the first impulse, this armature, through'the medium of the L-shaped piece 153, disengages the release-link 182 from the double-dog or lockin -device 164 allowing its arms 188 and 189, under the tension of the retractingspring 190, to fall against the circular and longitudinal teeth 201 and 204, respectively; the arm 1.88 looking the shaft in the position to which it is raised by the first step. On the second impulse, the shaft is raised again, and again locked by said arm 188 in the second raised vertical position.

At the end of this operation, the privats-wiper 208 and the line-wipers 210 and 211 will bev found on a level with the first contact of the second row of their re spective banks 209 and 213. Now, assume that the first nine trunks leading from the first nine contacts of the private and line banks 209 and 213 are busy, each of the trunk-lines leadin from said contacts being engaged by some SGCODCl-SiilEOtGl similar to the second-selector D and a guarding potential being established at each one of the first nine private-contacts of the second row of privatebank 209. The operator atsub-station A new pressing button 20 once, causes the rotaryline-conductor 31 to be grounded once, by causing spring 22 to come in contact with rounded sprin 25 after having disengaged with contact point 24. In this way, the rotary-1ine-relay 141 of the second-selector D is energized through the following circuit: from ground G at substation A, through the grounded contact 25 of the calling device, spring 22, line-conductor 31, springs 131 and 132, conductor 440,.rotary-line-wiper' 113 of the first-selector G, rotary-trunlr-coir ductor 489, springs 231 and 230, conductor 451, rotary-line-relay 141, conductors 444, 445 and 446 to the non-grounded terminal of battery 13, to ground G. The rotarylinerelay, thus energized once, attracts its armature 142, grounding spring 143 on spring 140, and energizing the private-magnet 191 through the following circuit: from ground G to springs 140 and 143, conductors 452 and 453, private-magnet 191, conduetors 454 nd 448; springs 1 131141 1 conductors 449 and 446 to the non-grounded springs 197 and 198 to separate, each engaging in turn with springs 196 and199, re-

spectively. Spring 197 being grounded at.

G, as soon as it comes in contact with spring 196 it energizes the rotary-inagnetcoils and 159 through the following circuit: from ground G te springs 19.7 and 196, to interrupter-springs 167 and 166, through rotary-inagnet-coils 160 and 159, conductors 45S and 448, springs 181 and 179, conductors 449 and 446, to the non-grounded terminal of battery B and to ground G. The rotary-1nagnet 158, being energized, attracts its armature 161. The rotary-armature-fingei 168 then depresses the privatearmature 192 and prevents'it from regaining normal position under the tension of springs 196 and 198, thus keeping springs 197 and 196 in contact with each other. The

'-interru'iter-tino'el." however eventual] 1 r; 9 a y separates springs 166 and 167, thereby opening the energizing circuit of the rotarymagnet. Meanwhile, the rotary-pawl 170 on the arm 169 rotates the shaft 200, so that the private-wiper 208 and the line-wipers 210 and 211 engage with the first contact oi? the second row of their respective,

at the instant the private-wiper 208 engages with the first contact of the second row of the private-bank 209, which is supplied with a guarding potential, the private-magnet 19.1 is again energized. In this way, the privatespring 196 is held in contact with the grounded private-' spring 197 while the rotary-arinature 161 is returning to its normal position. So as soon as the springs 166 and 167 come together, the rotary-magnet 158 is again energized. It again attracts its armature, rotating the shaft one more step, thereby pla ing the private-wiper 208 in engagement with the second contact of the second row of the private-bank, in which position the shaft is maintained by thelocking-arm 189 of the double-dog 184. Again the interrupter-springs 1'66 and 167 are separated by the interrupter-arm 165, again de-enen gizing the rotary-magnet 158, the rotary armature 161 falling back once more, This er ps ed as often a he e se-wip r encounters private-contacts with guarding potential.

When the shaft has. been rotated nine steps, the private-wiper.208 will be found engaged with the ninth contact of the second level of the private-bank. Now, when the rotary-armature is again actuated, it rotates the shaft to thetenth step, causing the priVate-wiper to disengage from the ninth. contact. In this way, the circuit through the private-inagnet 191 is broken, and becoming d e-energized it gives up its armature 192 to the control of the rotaryarniat-ure-iingei 168. Just at this time, the rotary-arn'iature being attracted, the private-armature is prevented from returning to its normal position, thus at once preventing springs 196 and 197 from breaking apart too soon. The interrupter-springs 166 and 167 will eventually engage again, but the design is such that this will not occur until after the spring 196 disengages from spring 197. At this point, the second-celectorwipers are engaging-the trunk-lines that lead from the tenth contacts of the second row of their respective banks. As soon as the shaft is rotated the first step,the cam 214i clears the cam-sprin 215, which latter then breaks from spring 217 and engages in turn with spring 216. It might appear that as soon as the cam springs 216 and 217 separate the 1ine-switolling-relay? 225 would be de-energized during rotation, but this is not so, for the energized condition is maintained by current from ground G through springs 19? and 196 to spring 216. After the rotary-magnet has ceased to rotate the shaft, and the privats-armature 192 regained its normal condition, a guarding potential is established at the privatewiper 208, and thereby at the private contact with which it is engaged, as well as at all other private-contacts connected in multiple. This guarding potential appears as soon as the priveto-wiper is ronnected with. the grounded terminal of lnittery, 1%, through the following circuit: from private-wipei" 208 to conductor 158, back-re ease-relay 220, conductor 4:59, springs 198 and 197, ground G to the grounded terminal G of battery 1%. At the instant that the private-arn'iature 122 regains its normalposition and contact be tween springs 19'? and 196 is broken the "line-switching-relay is 'de-onergized. The arn'iature 226 of this relay, returning to its normal position, disengages springs 231 and 228 from 230 and 227, bringing them in contact with springs 232 and 229, respectively. It is clear that as soon as the first-selector" C trunks to the second-selector D, the latter switchwhich'normally is otl' the line is automatically brought on the line and operated by the manipulation of the callingdevice corresponding to the second digit of the number being called.

The wipers of said "second-selector in' from across the main line, and extending the subscribers line to a connector E through the following path: from verticaL line-conductor 30 to springs 128 and 129 of the first-selector C, conductor 13?, vertical-line-wipei" 112, vertical-trunkconductor 4-88, springs 228 and 229, conductor 460, vertical-line-wiper 210, Vertical-trunit-conductor 161 to an idle connector, back over the rotary-trunk-conductor 462, "rotary-line-wipei" 211, conductor 163, springs 232 and 231, rotary-trnnl :-conductor 489, rotary-line-wipei 113 of the tirstselector C, conductor 14:0, springs 152 and 181 to the rotaryconducto1" 3 The subscriber at sub-station A having thus extended his lines to the connector, operates his calling device in accordance with the third digit of the number he is calling. He then presses the button 19 four times, grounding the vertical-line-conductor 30 four times in a manner already forth, energizing the vertical-line-relay oi" the connector E through a circuit as follows: from ground G at sub-station A to groundspring 25 ot the calling device, to conductor 30, springs 28 and 129 of the first-selector C, conductor 137, "vertical-line-wiper 112, "vertical-trunk-conductor 4-38, springs 228 and 229 of the secondselector ll), conductor 460, vertical-line-wiper 210, trunk-conductor 461, vertica.l-line-relay 235 of connector E, conductor lG-fl, to the nongrounded terminal of battery 13. Being thus energized, the i vertical line-relay 235 operates its armature 236 tour times, thereby ground ing spring 238 on spring 240 tour times and energizing, in turn, the vertical-mag net 24-5 through the following circuit: from ground G through springs 2 10 and conductor 4135, springs and 296, conductor 466, side-switch-wiper 324-, contach point 328, vertical-niagnet-coils 24-7 and 2 16, conductor 416 to the non-grounded terminal ot battery 13. This vertical-mag net, being energized, attracts its armature 248 tour times and, in the same manner as the first and second selectors, raises the shaft by a step-by-step motion. At the first in'ipi'ilse, the release-link 273 is disengaged from the double-dog" 276 by means otthe L-shaped piece .258, thus allowing the locking-arms 280 and 281 ot the latter, through the force of the retractirig-spring 282. to rest upon the circular and longitudinal teeth 301. and 304:, respectively. 'At the end of the fourth impulse, the wipers are on a level with the first contact of the tourth row of their respective banks; the private- Wiper, opposite the private-bank 3121;

i and the line-Wipers and 313 opposite armatureto itsnormal position.

439 to springs 231 and 232 of thesecond!- s elector D3,. conductor 41-63, rota-ry-line- Wiper 211, trunk-conductor 162, relay 241, to; the non-grounded terminal of battery B. In this Way, the armature 2 12 of. said ro tary line-relay is attracted once, thus grounding spring 243 with spring 2 10 once,

thereby energizing the privatemagnet 283 once. The energizing current passes from ground G through. springs 2-10 and 2&3, conductor 467,. privateunagnet' 283, con.- ductor 464-, to the non-grounded terminal. of battery B. The private-magi)ct, being thus energized, attracts its armature 284: and allows the side-sWitch-arm 320 to: disengage with: the tooth 291 and to fall against the tooth 292v on. its downward stroke. From the-latter it disengages on the returnv ofsaid Under the tension oi. the retracting-spring 321, this side-sWitch-a-rm is drawn forward: until the lug 322 strikes the earn 316. By this motion, the side switchrwipers 32 1 325,

326 and 32"? are disengaged from the con.-

tactepoints 328, 329, 330 and 331, With Which they normally close, and brought into en gagement, in turn, With contact-points 332, 333, 3345 and 335. tion- A; noW, for the last time, operates the calling device in accordance With the last digit of the number 224M, pressing button 19 once, and grounding the vertical-con ductor 30, as before. The vertical line-relay 235 is thus again. energized through the circuit that has been once described; This vertical-relay, on attracting its armature once, energizes the rotaryunagnet 2.58 once, by causing springs 238 and 24:0 to close. The circuit is as follows: from, ground G through springs 24-0 and 238, conductor 4e65, springs 297 and 296, conductor 466, sideswitchrarm 324, contact-point 332, coils 259* and 260 of rotary-magnet 258, con;- ductor e64, to the non-grounded terminal of battery In this Way, the armature 2.61 of the rotary-magnet 258 is operated once. The rotary-pawl 266, on engaging The operator at sub-sta-' 'ns-sass i.

with. thelongitudinal teeth 304e, rotates the shaft once, and the shaft is held in this retated position by thelockingarm 281 of the double-dog 27.6. In this Way, the privatewiper and the Fiine-Wipers are set on the first contacts of the fourth row of their respective banks, and. the cam moving out or the Way, the sidesWi-teh-arm then falls falls against the stop 345.. As'soon as the side-switch is brought into the third position, the side-switch-Wipers". 324i, 325, 326 and 327,011 disengaging from the contactpoints 332, 333, 334i and 335, close in turn With thecontaet-points 336, 337, 338and 339. At the instant that the side-switch.- Wipers 326 and 32'7 engage with the con.- tact-points 3'38 and 339,.the subscribers line is extended from blLlIIlii-COntlLlCtOlS 46-1 and 4562 to the line-Wipers 3.12 and 313,. and

thence through the"tnormal-trunk:conduc tors 168 and 169 to the called subscribers station. The extended circuit is from trunk-conductor 4561 to condenser. 366 and conductor 4:70,. springs363- and 36 1, sidevaWitch-Wipe?'326, contact-point 338, conductor 4:71,. verticaldineiper 312, conductor 168,' to the called subscribers'station and back over the trunk-conductor {69, -rotarydino-wipel" 313', conductor e72, contact-point 339T, sid'e-switcli-wiper springs 361 and 360, conductor 4573, c0ndenser 367, to conductor 462; Art the same time, a guarding potential is established at the private-Wiper 310, and thence at the first contact of the fourth row of the. private-bank 311, as Well as at all other multir .pled contacts, to temporarily prevent any other subscriber from intruding on the called line. This guarding potential reaches the u'ivate-Wiper through the folloWi-ng conductors: from grounded terminal G. of battery B, to ground G at the side switch, contact-point 337, Wiper 325, conductor 474:, private-Wiper 310, first contact 01 the fourth row 0t private-bank. 311, and. to all other contacts connected in multiple. This connection of the first contact of the fourth row of the private-bank. 311' With the grounded terminal otthe battery B.- (Fig. 2) causes the line-switching-relay of the first-selector of the called subscriber to be energized. The

circuit formed is from the grounded Wiper side-switch- It di'sengages from the.

ill)

310 to the private-nofinal-conductor 517, conductors 518 and 519, cam-springs 378 and 377, "line-switching-relay 398 of the called subscribers first-selector F, through the winding of the rotary-magnet too to conductors 520 and 521, to the non-grounded terminal of battery B, and to ground G. As soon as the armature of this "lineswitching-relay is attracted, it causes springs 396 and to separate from springs 39'? and 394. The separation of these springs removes a bridge composed of the rotary and vertical line-relays 386 and 385 of the first-selector F. This bridge is normally closed across the lineconductors 489 and are as follows: from conductor 489 through springs 393 and 3.94, rotarydine-relay 386, vertieal-linerelay 385, springs 897 and 396, and through the Vertical-linc-conductor 479. It is desirable to remove this bridge connection, so that there may be no hanger, when the ringing current is sent over the called subscribers line, of the line-relays beingenergized, as this might interfere with the established connection. The removal of this bridge is also desirable for the reason that any bridge across a talking line-circuit should be removed in order that no part of the Voice-currents be uselessly side-tracked or lost. As will later on appear, the conductors and 489 form part of the talkingcircuit when the subscribers begin to coinniunicate. The calling subscriber, having established connection with subscriber #:22 ll in the manner explained, is now ready to ring the bell at the called station. This is done by pressing the button 26 at sub-station A, which causes spring 29 to 29, 6 and 5, through contact-point 22-3, spring 21 to the verticaMine-conductor 80,

thence through a circuit already described, through the vertical-linc-relay 235 of the .connector E to the non-grounded terminal of the battery B. In this way, the vertical-line-relay actuates its armature, causthe ringer relay 358 to be energized. The circuit is from ground G to springs 240 and 238, conductor e05, springs 297 and 296, conductor l /d6, sideswitch-wiper 2324, contact-point 330, conductor 475, ringer-relay 358, conductor 4:76, conductor 464i, and to the non-grounded terminal of the battery l3. Thus energized, the ringer-relay attracts its arn'ia'ture 359, thus causing springs 361 and 864, respectively, to break from springs 860 and S03, and to engage in turn with springs 362 and 365. it is evident that the lirst two springs constitute the terminals of the called subscrihers line, while springs 360 and 363 constitute the terminals of the calling subscribers line, the springs 362 and 365 being the terminals of a dy amo M. Therefore, the function of the ringer-relay is to disconnect the caller line from the line calling, and to throw it across the terminals of the dynamo M, which latter then rings the bell 327, springs 361 and 362, conductor 490 to the brush and back to the dynamo M. The bell at sub-station $22M will now ring as long as the calling subscriber continues to press his signaling-button 26, or until the called subscriber removes his receiver from its hook. As soon, however, as the signaling-button is released, contact is broken between spring 29 and contact-point 28, thereby allowing the Vertical-1ilie-relay at connector E to be tie-energized, and in turn the ringer-relay 858. This will restore the connection between the tern'iinals of the called subscribers line and the terminals oi the calling subscribers line.

As soon as the called subscriber removes his receiver -l92 from its hook, the ringing circuit spring 48st breaks contact with the switclrhook 4553, thereby breaking the ringing circuit, and a moment later causing the following springs to close: 4-93 with 419st; 95 with 4:96; and 4:9? with 4-98; and placing the line-circuit in final condition for talking, The closing of the sruings l9?) and 496 closes a local circuit at sub-station S from the battery 499, through the transmitter 500 and the primary winding 50.1 at induction-coil 502, as tollows: from battery 1-99 to transmitter 500, springs 4-5 9 and 195, primary coil 501 and back to battery 499. Talking current being thus supplied, when the subscriber at sub-station S speaks into his transmitter 500, the resistance or the local circuit just described is varied, thereby causing the local current to vary, and to induce in turn currents in the secondary winding- 503 oi? the indin-tion-coil 502,, in a well-known manner. These induced currents reach the receiver of the calling subscriber through the seccanlary winding 503 oi the induction-coil 502, conductor 50+, receiver 492, conductor 505, contact-point 487, spring 488, rotary-hlie-conductor 4-89, irlink-conductor :69, rotary-linewiper 3L; oi connector E, conductor 4:72. contactpoint 339, side-switch-wiper 327, ringerthe ill? selectol C, c-ondluztor 44:0,.1ineswitchmg relay-springs 132 and. 131,. ro-

switch-wiper tary l-ine condzuctoi 31', spring 22, contactpoint 2 1, conductor 505, receiver 2, conductor 506,. secondary winding 18 0t inductuurcml 16,. contact-point 21', springs 29, 6 and'5, cone tact-polnt 23, spring 21, vertiealrlme-ccmductor. 30, 'line-switching-relaysprlugs" 128-2111611251 of the first-selector l, condnctor 137.. "vertical-line-wi-oer 11 2 verticmltrunleconductor" +138, line-switching reiaiy springs 228 and .2529: of the secondselector 1), conductor 460, vertical-linewiper 210,. "vertical-trunk-conductor 1-61, condenser 366- of: the connectol Fl, .comluctor 110,. 1. inger-relay-springs 363 and 364,. side- 2326,. contaotpoint 338, conductor 171, vertical-1ine-wiper S12, VQI tical-norn'ial; conductor 468, vertical-lineconductor 179, spring 180, contact-point 4181, conductor 482,.spri1ws 183,4195: and 50?,

i) and contact-point 508 tl n'ough. the secondary winding 503 of the induction-coil 502. In like manner, when the subscriber at station A; speaks into. his transn'iitt'er, the voice vibrations will be" reproduced the receirver 492 througli the same circuit just described.

The vibrations set up in the transmitter 141- I affect the local circuit of the battery 15, which induces currents in the secondary winding 18. After the conversation has'been completed, the switches may he released or restored: to their normal positions-by the subscriber at sub-station A in replacing hisreceiveron itshook.v This causes the arm 509 on the hook 3, on its downward course, to momentarilyv engage spring 1, pressingit iorward? toward: spring 12,so:that springs 11, 12, and: 1.3 willz he momentarily and: simultaneouslybrought into contact. This causes the vertical and rotaryline-conductors 30 and 31- to be momentarily grounded as follows: from ground G through springs 10' and 9, conductor 421,,springs13, 12' and 11, conductors 510 and 511., contact-points 23 and 21, springs 21' and122 to the line. The ground ing of the line-conductors causes the rotary and vertical line-relays 235 and 211 at the connector E. to momentarily attract their armatures 236 and 24-2, at the same time. In this way5springs 23 T and 239 arebrought into contact, there y energizing the release-magnet 268 01. said connector, and also the baclerelease-relay" of the second-selector D, as follows: from ground G at the secondselectoi D through springs 197 and 198, conductor 159, baclcrelease-relay" 220, conductor 1'58, private-wiper 208,. release trunk 512,

' meas es of the connector E', conductors .513 and. 514,. "release n'iagnet" 268, conductors 515i and. that to the nongrounded terminal; of the battery B, and to groui-id (Sc. Thus energized, the release magnet atracts its armature 269' with 'a. sudden jerk, kicking the double-dog 270 inwardly so that the zpertln-re2i5 ot the Frel'ease lin k 2Z3 falls over the h'lg-Q'IIT, thus holding, the locking-arms 280: and: 281 may from the circular and. longitudinal. teeth 30.1 and; 301. The shaft 300 thuslelt to the action of the coil-ermine, 305,. which. rotates it upon the shaft-rest 303 until the stoparm. 307 strikes the stop-post 306, at which instant therest 303' diisengages from: the circul'ar teeth by mentoring the channel 302 which traverses these teeth. The shaft then drops to its lhwestposition under the force 051? gravity, the arm 307 causing; the spring 2308 to separate from the contact-point 3'09; When the double-dog is thrust inwardly springs 287" and 239 I by the release-armature, its arm 3% drives the link 2313 before-it, causing the side switch. to rotate about the pivots 310" and 3411 against the pull of the retractingspri ng 321, and causingthe "side-switch.-arm to return to its first position. The side switchwiper 325,011: disengaging'trom t11e sideswitch-contacbpo-int" 337, removes guarding potential from the first contact of the. fourth row of the privatebank 311, which causes the Clo-energizing of the line-switching-rela y 398 oi't'the called first-selectofi F- In this way, the normally bridged line-relays that were removed from the line at the in:- stant the con'nectom established connection '7 are restored to the called line.

As was stated, the baclorelease-relay 22.0 of the sccond-selectol Dis energized simultaneously with the. releaseqnagnet 268 of the connector E,'itbeing= in the saane circuit; so that at the same time that the "connectorrelcase-magnet attracts its armature, the "hack-release-relay 220 also attracts its armature 221, causing the onerg-lzation of the .second=selector=release-magnet 1'75, and of the hack-re lease-relay of the first-selector G. In tl'iis-way, the "back-release-relaysprings 222. and 223 are brought into contact, and. the energizing circuit is as follows: from ground 'G" at the firstselector 0 through springs 109 and 108, conductor 4182, springs 97 and 98, conductor 4134:, backrelease-relay 120,. conductor 1451, privatewiper 110, release-trunk 4 12, conductor 51a, springs 228 and one, conductor 515, freleasemagnet 175, conductors 449 and 4416, to the non-grounded terminal of bat tery B, and to ground G. Thus energized, the release-magnet of the second-selector D, attracting its arn'iature 1T6, thrusts the ielease linlz 182 suitiicientiy forward, so that theaperture183 in theforward part i of the said link catches the doubledog 184 by means of the lug 185. Thedouble-dog is then rotated in such a manner upon the pivots 186 and 187, when the release-magnet becomes (lo-energized, as to draw the locking-arms 188 and 189 away from the circular and longitudinal teeth on the shaft 200, leaving said shaft to the influence or action. of the coil-spring 205. This spring rotates the shaft back on the shaft-rest 203 until the stop-arm 20E strikes the stop-post 206. At this uncture, the shaft-rest 203 disengages from the circular teeth and enters the channel 202, and allows the shaft of its own weight to fall to its restored position. At about the same time that the stop-arm strikes the stoppost, or normal post, as it is called, the cam 21 1 causes the camspring 215 to separate from spring 216 and to resume its normal connection with the spring 217. The back-release-relay 120 of the first-selector C being also energized, as stated, attracts its armature 121, in turn energizing the release-magnet 75 of the first-selector C. In this way, the springs 122 and 123 are brought into contact, and the first selector-release-magnet is energized'as follows: from ground G through springs 109 and 108, springs 123 and 122, conductor 516, release-magnet 75, conduc tors 427, 428 and 124;, to the n0n-grounded terminal of the battery B, and to ground G. Being thus energized, the release-magnet '75 attracts its armature 76, which causes the release-link 82 to take hold of the double-dog 84, just as was the case in the second-selector. The release-magnet, on being (ls-energized, restores its armature. The double-dog is then drawn away from the circular and longitudinal teeth, leaving the shaft to the tension of the coiled spring 105, which restores it to its normal position. Just about the time that the stop-arm 107 strikes the stop-post 106, the cam 116 separates the can'i-springs 117 and 118, thus breaking; the charged or energized circuit of the lineswitching-relay 125 and restoring it also to its normal position. The springs 131 and 128 then return into contact with the springs 130 and 127, respectively. Thus. it will be seen that at the instant the switch-hook at sub-station A closes the release-springs 11, 12 and 13 into contact, the energization of the rotary and vertical line-relays at the connector E, by closing contact between the springs 23'? and 239, causes the simultaneous energization of the connector-releaseunagnet 268, and of the second selector hack release relay 220. The back-release-relay in turn, by attracting its arnnlturc, causes the energization of the release-magnet of the second-selector D, and of the bacl-:release-relay of the first-selector C, which last relay by attracting its armature energizes the release-magnet of the first-selector C. All of these electro-magnets will remain energized as long as the release-springs at sub-station A remain in contact. The release mechanism of the connector differs from the release mechanism of the first and second selectors to this extent,that in the connector the "release-armature, on being attracted, by a thrust causes the release of the connector at once. The release mechanism of the second-selector, as well as that of the first-selector, however, does not restore the switch until after the release-magnet resigns control of its armature, and this occurs at the instant that the switch-hook at the releasing sub-station has fallen low enough to allow the releasesprings to disengage. At that instant, the vertical and rotary line-relays at the connector release their armatures, thereby allowing the springs 23'? and 239 to separate and break the circuit through the conneetor-release-1nagnet and the secondselector-back-release-relay, which relay at this point restores its armature.

The restoration of the back-release-relayarmature of the second-selector D allows the springs 2.22 and 223 in turn to disengage, thereby permitting the de-energization of the release-magnet of the second-selector D and of the "back-release-relay of the first-selector C. These last two electro-magnets at once restore their armatures. The restoration of the "secondselector-release-armature results in the restoration of the second-selector, as described. The restoration of the armature of the first-fie leetor-back-release-relay results in the deenergizing of the release-magnet of the first-selector C which latter relay, on restoring its armature, releases the switch in the manner explained. After the calling subscriber has released all the switches by the restoration ofhis receiver, the called sub scribe r restores his receiver. In the same manner, the release-springs 522, 523 and 52-1 of his substation close in momentary contact, sin'iultaneously grounding the conductors of his line from ground G through springs 198 and 197, conductor 525, springs F 523 and 52 1, contact-points 4:87 and 481, springs 188 and 480 to the line-conductors 4-80 and 4:79. The grounding of these conductors results in the energizing of the vertical and rotary line-relays of the iil'StSGlCt()l' F (Fig. As this firstselector F is similar to the fil'St-SQ-lGCtOl C, referring to the latter (Fig. 3), the grounding of these line-conductors has the same effect as if the vertical. and rotary linerelayi-x 35 and 41 were energized. Thus ei'iergized, these relays attract their armatures, thereby b lining the springs 3? and 39 into contact, which would energize the releaseanagnet 75 through the follow and to ground G.

479 and 489. denunwardly, the spr1ng524; comes into conmct Wl-tli, the spur-n53; 523, tl-ieireby grounding;

ed s

current tl' ing conductors: from ground G through I s arin s BT-end 39 conductor 5L6 release-- magnet"- 75, conductors 427, 428 and 424,150 the nongrounded terminal of the battery B, and to ground G. Tl'ius energized, the release-magnet would attract its armature 76, separating springs 79 and 81 on the back of said armature. As this switch is already released, this operation of the release-magnet has no etl'ectof in'iportance. The sepanation of :the springs 79 and 81, referred to,

is designed to prevent the vertical and course, this is due to the fact that the line- ;swltching-relay-sprlngs" 398 and 396 are separated from the neighboringsprings 394 and 897. Therefore, special provision has been IHZMlQ that a called subscriber may be able to release the switches that take part in maintaining a connection between a calling subscriber and his own line, in case the former should neglect to restore said switches after their use. For instance, it the subscriber at station A neglects to :release after ie is through talking, andfthe called subscriber should wish to make a call,

the latter will pull down the switchdiook 4:83 and thereby ground lllS line-conductors As the switch-hook travels the rerticsl-lineconductor" 4.79 by way (If ground G contact-points 4:98 and 49.7., conductor releese-spriugs 524-. and. 52; -contact-point 481, and spring 480. The result is that the hack-release-relay 3-18 becomes magnetized. The path tollmved by the current is from ground i to the vert-ical-lincconductor 41-79., norm:rltrunk-conchactor 41:68, .sidesxritch-wviper 326, li-ne-sw' ins-relay-spri-ngs 86-4; and 368, 00nd].

.4170, insole-release-relay 34.8, cond-iiictor 14:34:

to the nen-groiuided terminal oi. battery 15 The relay 348 being mew 1e .arnmtiuze 3 -9 pressesthc ground- 'ng 350 rig-sac st the spri 35]. An ener icing aircuiw .J thereby closed through the riarydine-relay 2st and thi-(ziug li the "reutical-line-relay 2853. The path oi": the uiough the former relay is ifironi ground through the springs 350 and 351, conductor 351, rotary-line-relay 241, conductor 464 to thenon-grounded terminal. of

netri-zed t1 spring 48 8, "rotaryline conducter meanest:

batter" 7 the cu. ent through the ertical-line-relay" extends from ground'G through the back- B ll l ltil tO ground G. The path of releasedelay-springs just described, over 211 ""verticah line-conductor 8( lineszwrtchrni erelay-sprmgs 128 and 1:29, conductor sot,"verrtical-liine-Wipei 112, Verticel-trunlr.-conductor 438, "ilii'le-switchingrelay-springs 228 and 229 of the secondselector 1);, conductor 466), vertical-line Wiper 2'16), "veuticelAt-runlvconducto'r 461, "vertical-line-relay? 235., conductor 46% to the non-grounded terminal of battery B and to ground G.

thei arn'iatures close the open contact between the springs 239 end 237, and therein. complete a circuit through the releaseniagnet 1268 of the connector. E and through the "hack-releaseielay 220 of the second- .SGlQCTOT JQ, as has. already been rdescnibed.

hut :the second-selector, and eventually the first-selector, :are released. fHowever, if tfior "any reason the circuit between the caliiing substation A and the co-nnect'or. has been 0.1f)enedf0r instance, by the blowing; of af-use-t'he connector E will Stll l be released, for as the switch-lwck 483 continues down, the three release-springs 522, 523 and 52st "are-flexed into co'ntsct, tl1e notary-lineconductoi 489 will ifllSO be grounded, and l'il'iC magnetized at thersz-unerelease-relay 34-8.

The {path the current The line-relays or the con inector" being thus energized simultaneously,-

llhe result is :that not only the connector hackn'elease-nelay" 352 will become une with the hacl;-'

will take through the said relay 3h2'is from c rround G through conductor 525, releases n-i-i'igs 524i, 523 and 522, contact-permt4 87,

nor1nal-trui"' conductor 4459, notary wipe-r 313 of connector ldlyeonductor .5 contact-point 339, side-sudtcheiviipefl 32?, ringer-relaysprings E361 and 4. 233, hsch-reilease-reiuy 352, :con. ctoi' 'rlli l to the noirgrounded terminal of battery B and to ground G. The HIlTIH tI G-S 34A) and 2 ii being attracted at the s: be time, the hack-release relaysrnrin-gs 5354), 313-1 35 i azre hfromghit into cor act and the neuter-1'e lease-mag net 268 will be en e1 thneugh a ("'l'cl'lll t beginisiing with groin-id (1 and tl ieneeithireugfh springs 350, 351 and 354-, conductors 518 and 514, "releaseenagnefi 268, conductor-s 51 5 and 464 to the non- .ohh coiiductor grounded terminal of battery B and to ground ()i'. in this last case the release magnet will he energized alone and not in series with the larch-release-relay ot the secondselector. The release-magnet being thus energized, the release mechanism of the coi'incctm. operated and the shaft restored to its normal position. As soon as the connector is released in either (it the above cases, the "priwite-wiper 310 breaks with the first contact of the fourth level of the private-bank 311, thereby destroying the energizing circuit through the lineswitching-relay 398 ot the first-selector F. The arn'iature of this relay will return to its normal position, as well as the line switching-relay-springs. The line-relays 385 and 386 being then restored to the line or sub-station #2241, the subscriber may then proceed to make his call.

Having once described the process by which one subscriber establishes connection with another, and the method of releasing the switches, it remains to assume case where a calling subscriber attempts to call a busy line. A line may be busy in either o't two ways, viz, by being called or by making a call. Suppose some one is con nected with substation #2241 at the time a subscriber at sub-station A attempts to connectwith the line of this substation There will be a connector similar to connector E, the wipers of which are set on the first contacts of the fourth row of their re spectire banks, and the side-switch of which is in the third position. A guarding potential exists, therefore, at this privatecontact. Now, this guarding potential extends not only to the "privatecontact-point" with which the occupied switch is connected, but to all others which, are in multiple. Ttheretore, every avenue through which a connect-or could establish connection with subscriber #2241 is guarded. New return to that stage of the call where the subscriber at sub-station A, in calling the subscriber at sub-station #22i1, had operated his switch, so that the first-selector" C, having been raised two steps and cut-in ten steps, had trunked to the "secondselectofi l); and where the second selector D, having been raised two steps and cutin or rotated t-ei'i steps, had trunked to the connector l and last. where the connector it had been raised four steps and cut-in one step, and (he sideswitch had been brought to the second position. The prirate-wiper, under these conditions, is in engagement with the tirst contact of the fourtl'i level o't its bank,

and the privateanagnet-spring 298 is in direct connection with the grounded terminal ot' the battery 13 as follows: from ground G through the occupied switch and a circuit (not. shown) to the 'tii'st contact 01 the fourth level of the private-bank 31.1, the privateoriper 474, sideswitch-wiper 325, contactpoint 00?} to spring 298. Now, as soon as the sub- ,Jcriber at substation A. presses button 20 or the last tune, so as to complete the connection, he grounds the rotary-iine-c n- 310, the conductor ductor Si in a welthnown manner, thereby energizing the rotary-relay ot the connectof 1*) which, in turn, by the actuation of its armature, energizes the pi'ivateinagnot 2823. As soon as the private-inagnet attracts its armature 28%, the arm 295 closes contact between the springs 298 and 299, at once energizing the release-ii'ia net 268. This releases the connectofi in a well known manner. The energization of the releascuiiagnet occurs through the tollow ing circuit: from. the grounded spring 298 (which was pointed out) through spring 295), conductors 525 and 51 i, release-magnet 268, conductors and 416 to the nongrounded terminal of the battery B, and to ground G. The calling subscriber, thinking that he has established connection, will press the signaling-button 26, grounding the verticai-line-conductor SO, therel'iy again energizing the yertical-line-relay at the connector. This relay, on attracting its armature, closes contact between springs 238 and 24:0 but by this time, instead of operating the ringer-relay, the side-switch being in the first position, the vertical-magnet 241:

is energized, causing the shaftto be raised.

Assoon as this occurs, springs 308 and 1309 close, thereby placlng a busy signal ap-" paratus across the line, which causes a buzzing sound tobe heard by the calling subscriber at his receiver 2. This busy signal apparatus is represented at H with one conductor-terminal 526 leading to the non-grounded terminal of the battery B, while the other teri'ninal. 52 leads to contact 309. This busy signaling machine may be ot any suitable, known or approved type, and connects with the calling sub; scribers receiver through conductor-terminal 52? through contact 309, spring 308, side-switch-contact-point 331, sidesi'vitch-wiper 327, ringc'-relay-springs 3G1 and 360, conductor 473, condenser 36?, rotary-trunh-conductor 4-62, iotarydinewiper 211 of the sccoiid-sclector 1), conductor 4.63, liiie-switching-reluy-springs 232 ant 231, rotary-trunk-conductor 43$), rotary-iilie-wiper 113 of the first-selector (l, conductor i l-l), lineswitching-relay-spriugs 132 and 1.3 linc-conductoi 31, spring 22, contactpoint 2t, conductor 505, receiver 2. conductor 5th, secoi'id'ai'y winding 18 of the induction-coil 16, contactpoint 27, spring 29 to springs 3 and 5, contact-point 233, spring 21, vertical-line-conductor 30, line-switching-relay-springs 128 and 129, conductor 413?, vertical-linewiper 112, vertical-trunloconductor 438,

lit) 

